1. Field of the Invention
The present invention concerns color management systems, and specifically concerns construction of colorimetric color appearance profiles and colorimetric color device profiles from spectral data. In particular, based on a spectral profile and on user input on viewing conditions, light source and media, a calorimetric color appearance profile and a colorimetric color device profile are constructed, so as to assure interoperability with color management systems which require both a colorimetric color appearance profile and a calorimetric color device profile for color management, such as the Windows Vista color management system and other similar color management systems.
2. Description of the Related Art
Currently, color management systems typically use colorimetric data values in order to convert from one color space to another. Usually, the colorimetric data is in CIEXYZ format. Color device profiles store values of the device's color characteristics. These values include a white point, colorimetric measurements and corresponding device values. The color device profile allows a device module to create accurate color mapping between colorimetric values under a specified light source and the device's values. In addition to the color device profile, a separate color appearance profile is provided which contains measurements of the viewing conditions under which a document is to be viewed. These measurements include a white point, and surrounding viewing information such as luminance level and the observer's level of adaptation. The color appearance profile allows a color appearance module to predict appearance of the output based on both the device's color characteristics and the viewing conditions.
Referring specifically to the Windows® Vista® color management system (WCS) as an example of a calorimetrically based color management system, WCS is designed to improve consistency and accuracy in color reproduction across different imaging devices. WCS is designed to work with calorimetric data for color management. WCS requires both a calorimetric color appearance profile and a calorimetric color device profile. Typically, a software takes the colorimetric color appearance profile and the calorimetric color device profile for a source device together with the corresponding colorimetric color appearance and device profiles for a destination device, and then using these four profiles processes the image data through WCS to convert color image data from the source device values (i.e. source color space) to the destination device values (i.e. destination color space).
WCS refers to these profiles as “color appearance model profile” (CAMP) and “color device model profile” (CDMP).
Currently, WCS standard output profiles are designed for certain viewing conditions, light source and media. Viewing conditions and light source affect both the colorimetry and the perception of colors dramatically. Also, different media significantly affect ink reflectance spectra. Every combination of viewing condition, light source and output medium is addressed by an appropriate pair of output profiles, namely a colorimetric CAMP and a colorimetric CDMP. For example, if the CAMP is for a D50 light source and an illumination level of 500 lux, then the CDMP should contain calorimetric values measured under a D50 illuminant. Building new profiles is complex, inconvenient and error prone. Correctness of profile pairing is not checked by WCS and mismatches of the profiles are possible.
The ability to adapt to new viewing conditions and media in WCS is limited. Currently, a change in viewing conditions or media has a system wide effect and requires changes in the system properties. For example, if a user chooses a certain CAMP for a printer, this CAMP will affect all printing devices installed in the system. This is sometimes undesirable.
The inventor has become aware of recent advances in color management systems which use spectral data rather than colorimetric data. A spectral device profile contains device values and corresponding spectral measurements. The advantage of spectral data is that the colorimetric values can be calculated for any light source, thereby providing a more flexible tool for color management and promising unparalleled accuracy in color reproduction and fidelity. The inventor has noticed, however, that spectral profiles are incompatible and cannot currently be used with WCS, or other similar color management systems.